The present invention relates to the measurement of pressure. Specifically, the disclosed embodiments describe an intravascular catheter tip pressure sensor but the present invention is not to be limited to the measuring of intravascular blood pressure.
Measurements of intravascular blood pressure are usually performed with a hollow catheter tube filled with saline solution and attached to an external transducer. This has the drawback of poor frequency response due to the long fluid column. In addition, saline solution is a poor dielectric, making electrical shock hazards a concern.
Catheter tip sensors have been proposed in which light from one or more fibers in a bundle is reflected off a mirrored diaphragm and back into different optical fibers. Pressure induced motion of the diaphragm modulates the intensity of the returned light which is then measured to infer pressure. One such pressure transducer is disclosed in the Strack U.S. Pat. No. 3,503,116 and its division U.S. Pat. No. 3,580,082.
In my earlier copending patent application Ser. No. 298,972, entitled "Fiber Optic Pressure Sensor", filed Sept. 3, 1981, now abandoned and assigned to the same assignee as the present invention, a fiber optic pressure sensor is described in which a reflecting diaphragm modulates the focal length of a lens-mirror combination. A pressure deformable single reflecting curved diaphragm is used as an optical element together with a lens or refracting element on the optical fiber end. The lens element collimates the cone of light emanating from the fiber and directs the light in a column towards the reflecting diaphragm, the diaphragm being separated by a very small distance from the lens. This refracting element on the end of the optic fiber preferably is a molded optical plastic lens such as a lucite member with a spherically curved surface.
In the present invention which is an improvement of my earlier copending application, above referred to, there is provided compensation for temperature as well as a reference sensor in addition to the earlier apparatus.